Auto Transmission Shifting Issue Since 4bbl Upgrade

You'll destroy the transmission if that "kickdown" linkage is not hooked up. That isn't all it does. It's more like a throttle position sensor too. Even if the 2-bbl linkage was somehow re-attached to the 4-bbl it probably can't/won't work right without the correct linkage. Read this article, and you'll have a good understanding:https://www.hotrod.com/articles/the-lowdown-on-stock-torqueflite-kick-down-linkage/